Multilayer films made from thermoplastics and having a release layer based, for example, on a silicone polymer are widely used as release films for adhesive tapes or self-adhesive labels, in order to prevent these single-sidedly or double-sidedly adhesive products from sticking to one another in the course of storage. A disadvantage of such release films, however, is that in the course of production, storage, and processing they undergo static charging and as a result suffer blocking, thereby hindering their processing. Since such unwanted static charging occurs in particular via the release layer, especially based on a silicone layer, discharging may be accompanied by at least partial destruction of the release layer and by blocking of the layer of adhesive by the damaged silicone layer.
Typically, therefore, antistatically equipped release films are used in order to avoid instances of static charging in the course of production, processing and/or storage.
Antistats are substances which are incorporated for instance into a plastics material or are applied to the surface of a plastics article in order to reduce electrostatic charging, thereby making it possible to reduce not only dust attraction but also spark discharge. The electrostatic charging of a plastic can be reduced by raising the surface conductivity or the volume conductivity.
The prior art already discloses release films which are antistatically equipped.
Thus EP 0 445 744 A2 describes a multilayer polyester film with antistatic effect which in addition to the release layer has a further layer comprising a cationic quaternary nitrogen compound as antistat.
US 2006/0222867 A1 describes a multilayer film which as well as the release layer has a further layer which comprises an alkoxylated amine as antistat.
A disadvantage affecting release films equipped in these ways is that their antistatic effect is not long-term, but instead is merely temporary. Moreover, as a result of their tendency to migrate into other layers of the release film, the antistats used may have negative consequences for the release properties and/or for the tensile strength and/or for the adhesion of the layer assembly of the release film. This may occur especially in the case of multilayer release films in which the antistats have been incorporated into an inside layer and are therefore able to migrate outwardly through a number of layers. These negative consequences usually increase in proportion to the amount of antistats that are employed, and so for that reason as well their proportion, relative to the release film as a whole, is to be minimized.
There is therefore a need for release films which do not have the disadvantages identified above.
It was an object of the present invention, therefore, to provide a release film which in spite of a sufficient long-term antistatic effect has no more than a negligible influence on the release properties and mechanical properties as a result of the antistat.